This invention relates to methods and apparatus for obtaining hydrocarbons from hydrocarbonaceous solids. In one aspect, this invention relates to methods and apparatus for facilitating the retorting of hydrocarbonaceous materials to produce useful hydrocarbons. In another aspect this invention relates to the destructive distillation of hydrocarbonaceous solids such as oil shales, tar sands, coal, lignite, peat, and the like. In another aspect this invention relates to means to counteract coalescing or swelling conditions in retorts.
Certain sedimentary rocks, commonly referred to as oil shale, on destructive distillation will yield a condensable liquid which is referred to as a shale oil and noncondensable gaseous hydrocarbons. The condensable liquid may be further refined into products which resemble petroleum products.
Other types of carbonaceous materials, both as an inclusion in rock, shale, sand, etc., or as a relatively low gangue content carbonaceous material, can be treated in a heating process for the recovery of valuable products. Such materials as coal, tar, tar sands, asphalts, peat, and the like are amenable to heating processes, to produce gases as well as hydrocarbonaceous liquids.
In its fundamental aspects, the destructive distillation of oil shale, or other solid hydrocarbonaceous materials, involves heating the solid material to a proper temperature and recovering the products which are emitted. In various attempts at retorting to date, the most common approach is the heating of beds of relatively small particulate oil shale and providing a stream of hot gas flowing through the shale bed. Since a solid and a gas are the major components of the system, countercurrent operation is the most conventional process encountered in the prior art. Because the destructive distillation takes place at a relatively high temperature, thermal efficiency dictates that the exhausting off gas and the exhausting spent shale leave the reaction vessel at a relatively low temperature. Various countercurrent retorting processes have been described, including one in which solids are mechanically moved upward and hot gases plus the retorted oil move downward, as described in the Synthetic Fuels Data Handbook, (Cameron Engineers, Inc., Denver, Colo., 1975) pp. 70-73.
From a practical consideration of the various processes, it has been found that the retorting should generally include a downward gravity feed of the solids through the retorting vessel and an upward rising gas and entrained liquid flow. This situation utilizes incoming cold solids to cool the rising stream of gases so that it leaves the bed at a relatively low temperature. In the same manner incoming gases are brought into the lower part of the solids bed to cool the retorted solids and to heat the gases to a desired temperature.
From a practical consideration, an effective oil shale retorting process has been achieved in a vertical shaft kiln by a gravity flow, continuously moving shale bed in the kiln. A constant height bed is produced by feeding solids to the top of the bed and withdrawing solids from the bottom to maintain the uniform depth of the bed. The retort includes at least three vertically aligned zones, for example a top preheating zone for the shale (which, also, provides for the disengagement of the products of the pyrolysis from the raw shale), a mid zone for pyrolysis and a lower cooling zone below the pyrolysis zone. In addition, fresh shale at relatively unelevated temperatures falls onto and resides materially on the top preheating zone. This process utilizes incoming ambient temperature solids to cool the rising stream of the produced products from the pyrolysis, so that the product streams leave the bed at a relatively low temperature. For an economic heat balance, the shale leaving the pyrolysis zone is cooled by bottom injected, incoming cool gas. This gas is heated by the hot shale and rises up through the particulate oil shale, through the retorting zone and is subsequently withdrawn as off-gas with the produced pyrolysis products.
Generally speaking, two major processes have been proposed for pyrolysis reactions in the vertical or shaft kiln, the first being a direct combustion process in which residual carbon on the shale is burned in the kiln, producing the heat for the pyrolysis, and the second being an indirect heat retorting in which a non-oxygenous gas is heated externally of the retort and is introduced immediately below the retoring zone, with the incoming heated gas being of a sufficient temperature to produce pyrolysis.
It has been noted, e.g. in U.S. Pat. No. 4,116,810, Column 4, that operation of an oil shale retort or kiln in an indirect heat retorting mode tends to produce cracking, coking and a general coalescing of solid material in the retort. Such coalescing can form agglomerates which impede the flow of the shale through the retorting zone, whether by gravity or mechanical feed. When a viscous liquid contacts solids a mass sometimes forms exhibiting very high apparent viscosities and which has a tendency to be immovable, thus bridges over or impedes the normal movement and flow of solid and liquid within the retorting apparatus.
Similar problems are encountered in the retorting of other hydrocarbonaceous solids, e.g. the fixed bed coal gasifiers described in U.S. Pat. No. 4,134,738. In addition to the formation of clinkers, or coal residues which have become fused together, when coal is heated in the absence of oxygen, the coal structure expands, or swells. The free swelling index is used as a measure of the amount of swelling experienced by the coal. Generally, the use of coals with free swelling indexes of greater than about 2.7 is regarded as impractical in certain types of fixed-bed gasifiers, since the coal will swell and plug the distillation zone of the gasifier. However, by agitating or poking such a coal bed, the gases causing the swelling can be released from the coal structure, thus permitting the use of coal with relatively high free swelling indexes in either fixed-bed or gravity-feed gasifiers.
Various devices are available for agitating beds of solid particles in heated retorts. For example, Bress et al discloses in U.S. Pat. No. 4,134,738 (1979) an automatic poking system for a fixed-bed coal gasifier in which multiple poke rods are actuated in a reciprocating manner to agitate the coal bed. Davis discloses in British Patent Application No. 2,081,432 (1982) a similar poking system for such coal gasifiers in which at least one reciprocable pokerod is mounted on a movable carriage to permit its use at multiple pokeholes in the retort. Despite the extensive development of such apparatus, there is a need for simple yet effective systems for agitating beds of solids in various types of retorts.
In oil shale retorts, whether directly or indirectly heated, operation of the retort tends to produce a relatively shallow zone above or below the retorting zone where viscous liquids come in contact with solids to form bridges or agglomerates which impede the flow of oil mist and gases as well as the movement of shale particles. This zone will hereinafter be referred to as the "viscous bridging zone" in reference to various retorts for processing hydrocarbonaceous solids as well as specific oil shale retorts. In a vertical, gravity-feed retort, there is generally a layer of fresh oil shale on top of the viscous bridging zone. There is a need for improved methods of agitating such viscous bridging zones to facilitate the flow of oil mist, gases and shale particles.